I wanted to share my efforts in building an inexpensive but competent belt driven camera slider. http://www.midwestlenticular.com/diy-camera-slider It uses the Opteka 47" rail but could be easily be modified to use an IGUS rail or similar. It has a variable speed controller that operates bi-directionally and can lift 5lbs vertically without stalling. Best of all the parts can be found through only 2 suppliers, Amazon and Servo City. The downshot is that while the motor is quiet it is not silent, as you can hear in the videos, though this seems to be true for most DIY rigs from what I can tell. Total parts cost is just over $250. Love to hear your thoughts!